Many mobile devices have braking systems to aid in stopping the device when it is moving. Braking systems typically apply friction to rotating wheels or axles to inhibit further rotation. Other braking systems generate friction by engaging the ground. See e.g. U.S. Pat. Nos. 1,311,998, 1,990,101, 2,049,357, 2,687,191, 2,703,632, 3,994,369, and 6,401,876, which are hereby incorporated by reference. Typical braking systems for modern, powered, wheeled devices use hydraulic pressure to actuate a service brake mechanism.
Representative examples of hydraulic braking systems include, without limitation, the braking systems disclosed in U.S. Pat. Nos. 3,945,685 3,945,691, 3,946,642, 4,736,991 and 4,792,192, which are hereby incorporated by reference. A typical hydraulic braking system has a source of hydraulic pressure that is operatively connected to hydraulically actuated service brakes via hydraulic lines. The hydraulic braking system is typically operated by a foot pedal, the actuation of which allows hydraulic pressure to actuate the service brakes. However, a loss of hydraulic pressure can lead to brake failure and, subsequently, a run-away device, typically a vehicle.
To prevent run-away vehicles, backup hydraulic systems have been used. U.S. Pat. Nos. 4,736,991 and 4,792,192, which are hereby incorporated by reference, disclose some such systems. However, for various reasons, these backup systems require the presence of extra pressurized tanks for the storage of reserve hydraulic pressure. The extra space requirements for such tanks can make them unsuitable for vehicles where space is at a premium or where the vehicle is used in conditions or in a manner where puncture of a reserve tank could occur. Furthermore, such tanks are limited in the number of actuations they can provide and may become depleted due to seepage or leaks. Moreover, such systems typically lose all pressure when disconnected from the hydraulic supply. Lastly, such extra tanks and the associated hydraulic lines and valves, etc. may significantly increase the cost of such vehicles.
Other known braking systems include ground engaging braking systems. Some of these systems are hydraulically powered (e.g. U.S. Pat. Nos. 2,049,357, 2,687,191, 3,994,369, and 6,401,876); while others are mechanically engaged (e.g. U.S. Pat. Nos. 1,311,998, 1,990,101, and 2,703,632). However, these vehicles are either also reliant on hydraulic pressure or, the case of mechanically engaged brakes, may provide insufficient mechanical advantage to quickly stop a heavy or fast moving vehicle.
An improved braking system that uses available non-reserve tank hydraulic pressure would be an improvement. Such a system that deployed a ground engaging brake upon utilization of that stored hydraulic pressure would be a further improvement.